Tuesday, October 18, 2016

Hottest September on record

According to GISS NASA, the average global surface temperature anomaly for September was 0.91 °C, which is just 0.01 °C higher than the previous hottest September in 2014.

The average for the eight months to the end of September is 1.03 °C, which is 0.23 °C higher than the previous hottest January to September period in 2015, which with the latest data had an anomaly of 0.80 °C.

There are now twelve in a row of "hottest months" from October 2015 to September 2016 (that is, hottest October, hottest November etc). If we could look back over the entire Holocene, it's probably more than 7,000 years since there was a similar run of hottest months on record, that is, not since the Holocene climatic optimum (it's probably hotter now than it was back then).

Update: It's just been pointed out to me that the latest revisions put June 16 temperature (0.75 C) below that of June 98 and June 15 (equal 0.78 C). That means that there were now eight months in a row of "hottest" - from October to May inclusive. Then another three hottest months from July to September.

Sou 10:54 am AEDT 18 October 2016

Here is a chart of the average of 12 months to September each year. The 12 months to September 2016 averaged 1.03 °C above the 1951-1980 mean and was 0.23 °C hotter than the 12 months to September 2015:

Figure 1 | Global mean surface temperature anomaly for the 12 months to September each year. The base period is 1951-1980. Data source:GISS NASA

Below is a chart of the month of September only. Hover over the chart to see the anomaly in any September:

Figure 2 | Global mean surface temperature anomaly for the the month of September only. The base period is 1951-1980. Data source:GISS NASA

Now no La Niña?

You can see the global mean temperature trend by month in the chart below, for the strongest El Niño years since 1950, which were followed by a La Nina. I've included the 2015/16 period for comparison. NOAA has put back the La Nina watch. The BoM ENSO update is still on watch status (it never came off).

Not counting 2015/16, of the seven very strong, strong and strong to moderate El Ninos since 1950, there were only three that were followed by a La Nina. The chart spans a three year period. That is, for the 2015-16 El Niño and subsequent, it goes from January 2015 to December 2017, or would if the data allowed. (For a more detailed explanation see the HW articles: El Niño to La Niña years with more detail here.)

Figure 3 | Global mean surface temperature for strong or moderate/strong El Nino years that were followed by a La Nina. Data source: GISS NASA

Where was it hot?

Last month it was again hot almost everywhere. Much of the northern hemisphere was very hot. Part of Antarctica is extremely hot and part is rather cool. There was also a cool patch over south-west Western Australia, which IIRC had the coldest September ever. The cooler patch south of Greenland is still there, too.

Year to date average surface temperature

The chart below tracks the year to date. Each point on the plot is the average of the year to that month. For 2016, the last point is the average of all months to date including September. This year is tracking well above 2015, partly because of the El Niño. To drop below the average for 2015, the average anomaly for the next three months would need to be less than 0.39 °C:

The next three months would have to be the temperatures of 16 years ago...

Given the expectation that this will be another "hottest year", below is a chart showing the average temperature for the three months from October to December from 2000 onwards. Only one year had the October to December average below 0.39 C and that was 16 years ago in 2000. (The red line is the average year to date for 2016.)

Figure 7 | Global mean surface temperature anomaly for the three months from October to December. The base period is 1951-1980. The red line is the average year to date for 2016. Data source:GISS NASA

9 comments:

It's just been pointed out to me that the latest revisions put June 16 temperature (0.75 C) below that of June 98 and June 15 (equal 0.78 C). That means that there were now eight months in a row of "hottest" - from October to May inclusive. Then another three hottest months from July to September.

I'll bet that there are no howls of protest from the Denialati about revisions that take 'record' months (or other warming signs) out of the, erm, record.

Of course a pedant would point out that such record events are in large fashion arbitrary subdivisions of time. As a counting and categorising species though it's an entirely natural thing to do, but perhaps it's salient for the punter on the street to keep in mind at least the general import of the statistical aspects of the underlying phenomena - both the fundamental signal/forcing that's driving the trajectory, and the superimposed modifiers that provide some of the 'noise' in the system.

The message that comes out at the other end once one accounts for what's actually happening is - "uh oh..."

Just to add to my comment about arbitrary subdivisions, I think that a case could reasonably be made for quarterly descriptions of temperature trajectory. These do smooth out the noise inherent in shorter increments of time, though not completely, but for those really noisy superimpositions there's always Tamino...

Well, here's kind of a bummer. If you look at the GISS data now, you will see that June 2016 no longer holds the June record. June 2016 currently (as of Oct. 17th 2016) reads 0.75 deg. C., while June of both 2015 and 1998 have anomaly values of 0.78 deg. C. I think this is either because the values vary by .01 to .02 deg C each month due to homogenization of the data or possibly because June was adjusted downward a little after the initial value was reported. A very minor thing, but it’s liable to be noticed and pointed out as a big hairy deal if it is not acknowledged now.

If the anomalies for the next three months stay around 0.9C, we'll hit a full 1C average anomaly for the year. For the seasonal year (Dec through Jan), it would just take 0.78C anomalies for the next two months.

I can picture global warming den... sorry, 'skeptics' keeping a low profile until it becomes clear that 2017 will be cooler that 2016. And then, cries of 'El Niño!' and 'No warming since March 2016!' will ring out from their aging, shrunken ranks.

The Perth WA September weather isn't as bad as the news reports would have you believe. The full quote from Neil Bennett (BoM spokesman and meteorologist) is:

"We've had the coldest September since records started at the Mt Lawley (Perth metropolitan) station in 1994."

So the coldest since since the official site of Perth's weather station moved to Mt. Lawley in 1994 - not exactly 'since records began.'

Needless to say, the West Australian letters to the editor had a few contributions from people who think that Perth's September temperatures negate the entire temperature records of the whole planet. There was even a 'no warming for the past 18 years ...' recently.

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